Lithographic apparatus, device manufacturing method and apparatus for de-gassing a liquid

ABSTRACT

A lithographic apparatus is disclosed that has a semi-permeable membrane, a liquid inlet adapted to supply liquid to a first side of the membrane, and a gas inlet adapted to supply to a second side of the membrane either: (a) a vapor of the liquid, or (b) a gas which dissociates when dissolved in the liquid.

FIELD

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device and an apparatus for de-gassing a liquid.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate (the substrategenerally has a larger surface area than the final element of theprojection system). One way which has been proposed to arrange for thisis disclosed in PCT patent application publication WO 99/49504, herebyincorporated in its entirety by reference. As illustrated in FIGS. 2 and3, liquid is supplied by at least one inlet IN onto the substrate,preferably along the direction of movement of the substrate relative tothe final element, and is removed by at least one outlet OUT afterhaving passed under the projection system. That is, as the substrate isscanned beneath the element in a −X direction, liquid is supplied at the+X side of the element and taken up at the −X side. FIG. 2 shows thearrangement schematically in which liquid is supplied via inlet IN andis taken up on the other side of the element by outlet OUT which isconnected to a low pressure source. In the illustration of FIG. 2 theliquid is supplied along the direction of movement of the substraterelative to the final element, though this does not need to be the case.Various orientations and numbers of in- and out-lets positioned aroundthe final element are possible, one example is illustrated in FIG. 3 inwhich four sets of an inlet with an outlet on either side are providedin a regular pattern around the final element.

One or more unexpected problems may emerge from this new immersionlithography technology when compared with ‘dry’ lithographic apparatusthat do not have liquid in the exposure radiation path. On possibleproblem is that, despite the improved resolution, the liquid may tend todegrade the image quality in other respects. In particular, bubbles inthe immersion liquid may reduce the quality of the imaged pattern.

SUMMARY

Accordingly, it would be advantageous, for example, to provide forde-gassing of a liquid to be used in immersion lithography.

According to an aspect of the invention, there is provided alithographic apparatus, comprising:

a semi-permeable membrane;

a liquid inlet adapted to supply liquid to a first side of the membrane;and

a gas inlet adapted to supply to a second side of the membrane either:

(a) a vapor of the liquid; or

(b) a gas which dissociates when dissolved in the liquid.

According to an aspect of the invention, there is provided a devicemanufacturing method, comprising:

transferring a pattern from a patterning device through a liquid onto asubstrate, wherein the liquid was provided on one side of asemi-permeable membrane and a gas provided on another side of thesemi-permeable membrane, the gas being either a vapor of the liquid or agas which dissociates when dissolved in the liquid.

According to an aspect of the invention, there is provided an apparatusconfigured to de-gas a liquid, the apparatus comprising:

a semi-permeable membrane;

a pump configured to provide the liquid to a first side of the membrane;and

either

(i) a vaporizer configured to provide vapor of the liquid to a secondside of the membrane; or

(ii) a gas inlet configured to provide a gas which dissociates whendissolved in the liquid and an ion exchanger for the liquid downstreamof the semi-permeable membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 6 depicts an apparatus for de-gassing a liquid according to anembodiment of the invention; and

FIG. 7 illustrates another apparatus for de-gassing a liquid accordingto an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam B (e.g. UV radiation or DUV radiation).    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PS configured to project a pattern imparted to the radiation        beam B by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more support structures). In such“multiple stage” machines the additional tables or support structuresmay be used in parallel, or preparatory steps may be carried out on oneor more tables or support structures while one or more other tables orsupport structures are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT mayberealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another immersion lithography solution with a localized liquid supplysystem solution which has been proposed is to provide the liquid supplysystem with a liquid confinement structure which extends along at leasta part of a boundary of the space between the final element of theprojection system and the substrate table. Such a solution isillustrated in FIG. 5. The liquid confinement structure is substantiallystationary relative to the projection system in the XY plane thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). See, for example, U.S. patent application Ser. No.10/844,575, hereby incorporated in its entirety by reference. A seal istypically formed between the liquid confinement structure and thesurface of the substrate. In an embodiment, the seal is a contactlessseal such as a gas seal.

Referring to FIG. 5, reservoir 10 forms a contactless seal to thesubstrate around the image field of the projection system so that liquidis confined to fill a space between the substrate surface and the finalelement of the projection system. The reservoir is formed by a liquidconfinement structure 12 positioned below and surrounding the finalelement of the projection system PL. Liquid is brought into the spacebelow the projection system and within the liquid confinement structure12. The liquid confinement structure 12 extends a little above the finalelement of the projection system and the liquid level rises above thefinal element so that a buffer of liquid is provided. The liquidconfinement structure 12 has an inner periphery that at the upper end,in an embodiment, closely conforms to the shape of the projection systemor the final element thereof and may, e.g., be round. At the bottom, theinner periphery closely conforms to the shape of the image field, e.g.,rectangular though this need not be the case.

The liquid is confined in the reservoir by a gas seal 16 between thebottom of the liquid confinement structure 12 and the surface of thesubstrate W. The gas seal is formed by gas, e.g. air or synthetic airbut, in an embodiment, N₂ or another inert gas, provided under pressurevia inlet 15 to the gap between liquid confinement structure 12 andsubstrate and extracted via first outlet 14. The overpressure on the gasinlet 15, vacuum level on the first outlet 14 and geometry of the gapare arranged so that there is a high-velocity gas flow inwards thatconfines the liquid.

An embodiment of the present invention relates to an apparatus forde-gassing a liquid. The apparatus may either be a stand alone apparatusor coupled to a lithographic projection apparatus. The de-gasser may beused to de-gas liquids such as photo-resist used in lithography.However, an embodiment is particularly suited for de-gassing immersionfluid which will be used in immersion lithography. In immersionlithography, immersion liquid is typically positioned between the finalelement of the projection system PS and the substrate W.

U.S. patent application Ser. Nos. 10/860,662 and 10/924,192, both ofwhich are incorporated herein in their entirety by reference, discussthe use of bubble reduction apparatus to reduce the occurrence ofbubbles in immersion liquid. In these bubble reduction apparatus, liquidis passed past a semi-permeable membrane which has pores which theliquid molecules cannot pass through. In this way the liquid isde-gassed. In an embodiment, the process is accelerated by applying tothe outside of the tubing a low pressure.

Membranes are used for removal of gasses from liquids in fields such asmicroelectronics, pharmaceutical and power applications. The liquid canbe pumped through a bundle of semi-porous membrane tubing (shownschematically in FIG. 7) using, for example, a pump. Thus the liquid isde-gassed. The process may be accelerated by applying to the outside ofthe tubing a low pressure. Liqui-Cel (™) Membrane Contractors availablefrom Membrana-Charlotte, a division of Celgard Inc. of Charlotte, N.C.,USA are suitable for this purpose and for an embodiment of the presentinvention as are Mykrolis Phasor II (RTM) membranes or Fiberflo (RTM)membranes from Minntech. Membranes which are made of a liquidphobic(e.g., hydrophobic) material are advantageous; the pores in the membranemay be larger than the liquid molecules but, because of the surfacetension of the liquid, they cannot pass the membrane. Such membranes aretypically only suited for use with liquids with a relatively highsurface tension such as water.

A problem with the foregoing method is that the amount of dissolved gasin the liquid is proportional to the saturation concentration of theconcerned gas in the liquid and the pressure of that gas on the otherside of the semi-permeable membrane. This means that the gas contentwhich remains in the liquid is proportional to the saturation level andthe applied vacuum level. If on the gas side of the membrane, a vacuumis applied without or with a very small gas flow past the membrane,diffusion of the gas out of the liquid through the membrane will limitthe lowest achievable partial pressure level of the gas at the gas sideof the membrane. However, even with a gas flow, the amount of de-gassingachievable is limited. In the case of applying a vacuum to one side ofthe membrane which is below the vapor pressure of the liquid to bede-gassed, the semi-permeable membrane is blocked by vapor of the liquidand so the de-gassing process does not continue. This limits the levelof vacuum which can usefully be used and thereby the lowestconcentration of gas in the liquid.

The examples given below are all for water as the liquid, but anembodiment of the invention is applicable to any liquid, such as a topcoat. By providing an inert or other stable gas, such as nitrogen, atambient pressure on one side of the semi-permeable membrane, the totalgas concentration in parts per billion in the liquid can be 19000 partsper billion. If an inert or other stable gas, such as nitrogen, is usedwith an under-pressure below atmospheric pressure in the region of 3000Pa (0.3 atm) (i.e. just under the vapor pressure of water which is 2700Pa), for example, the concentration of gas in the liquid can be reducedto as little as 578 parts per billion. If a vacuum alone is used (3000Pa or 0.3 atm), the concentration of gas can be reduced to 727 parts perbillion. However, these levels may not be considered low enough and anembodiment of the present invention can achieve a total gasconcentration in the liquid of below 200 parts per billion and in someembodiments lower than 50 or even lower than 5 parts per billon. As willbe appreciated, any under pressure will help reduce the concentration ofgas in the liquid, even 0.95 atm.

An embodiment of the apparatus of the present invention is shownschematically in FIG. 6. Liquid to be de-gassed is provided to a inlet100 and flows past a semi-permeable membrane 120. After being de-gassed,the liquid proceeds to outlet 140. A chamber 125 may be providedadjacent the semi-permeable membrane so that liquid spends more time inthe vicinity of the semi-permeable membrane 120. A gas is provided toinlet 200 and forced to flow past the semi-permeable membrane 120. Thegas continues to exit 240. The gas may either be allowed to escape tothe atmosphere or be re-cycled. The gas can be provided at an underpressure, at a level at least above the vapor pressure of the liquid.

In a first embodiment, the gas which is provided on the side of thesemi-permeable membrane 120 opposite to that of the liquid to bede-gassed is vapor of the liquid to be de-gassed. In this instance, itis possible to reduce the concentration of gas in the liquid to below 50parts per billion. A concentration of 36 parts per billion istheoretically possible. A typical gas flow rate would be 2 L/minute anda typical liquid flow rate would be 1 L/minute with a semi-permeablemembrane surface area of about 1 m², depending on the level ofequilibrium which it is desired to achieve. An optimal range of flowrate would be between 0.1 and 10 L/minute and a surface area of themembrane of 0.5 to 5 m² could typically be used.

In this embodiment, it is possible to provide a single liquid inlet 300which provides liquid to both inlets 100 and 200. A liquid vaporizer 250is provided between the inlet 200 and the semi-permeable membrane 120 tovaporize the liquid. A condenser may be provided downstream of outlet240 so that the liquid may be re-cycled. In an embodiment, the liquid iswater.

By using the vapor of the liquid as a sweep gas to de-gas the liquid, aflow is generated at the gas side of the membrane causing lower partialpressure gas to be removed from the liquid at the gas side of themembrane. Because of the lower partial pressure level at the gas side,the liquid is de-gassed to a significantly lower level than when avacuum is applied or a sweep gas is used from a composition other thanthe liquid vapor. This means that de-gassing may be orders of magnitudemore effective than using only a vacuum or an inert or other stable gasas a sweep gas.

In a second embodiment, the gas which is used on the side of themembrane 120 opposite to the liquid is a gas which dissociates into ionswhen dissolved in the liquid. A good example of such a gas is carbondioxide (when the liquid is water). A flow of carbon dioxide isgenerated on the side of the membrane 120 opposite the liquid and thiscauses a significantly lower partial pressure gas to be removed from theliquid. Thus, by using carbon dioxide under a low supplied pressure, thepartial pressure of all other contaminants is equal to the suppliedpressure times the contamination level in the carbon dioxide. Thus, thepartial pressure of nitrogen in a carbon dioxide sweep gas at 3000 Pawith 5000 ppm nitrogen is 15 Pa. Because of the lower partial pressurelevel at the gas side of the membrane, the liquid is de-gassed to asignificantly lower level than when a vacuum is applied at the gas side.A gas that dissociates into ions when dissolved in liquid will beabsorbed through the membrane into the liquid, but may later effectivelybe removed by means of an ion exchanger 150 which is provided downstreamof outlet 140. The level of de-gassing may be reduced even further byapplying the carbon dioxide at an under-pressure. The following tableshows the theoretical lowest achievable equilibrium concentrations undera variety of conditions using carbon dioxide to de-gas water using ahollow Teflon fiber membrane.

Pressure Concentration of gas in Gas (atm) liquid (ppb) Liquid vapor0.03 36 CO₂ (5000 ppm purity) 1 121 CO₂ (5000 ppm purity) 0.03 3.6 CO₂(80 ppm purity) 1 0.48 CO₂ (80 ppm purity) 0.03 0.015The results in Table 1 are calculated on the basis of an infinitesemi-permeable membrane contact area.

A further refinement of an embodiment of the apparatus according to theinvention is illustrated in FIG. 7 in which like reference numeralsindicate similar objects to those in FIG. 6 and in which it can be seenthat a plurality of tubes are provided, all of which are made of asemi-permeable membrane. This is one way of increasing the surface areaof the semi-permeable membrane and therefore the efficiency of thede-gassing process.

In European Patent Application No. 03257072.3, the idea of a twin ordual stage immersion lithography apparatus is disclosed. Such anapparatus is provided with two tables for supporting a substrate.Leveling measurements are carried out with a table at a first position,without immersion liquid, and exposure is carried out with a table at asecond position, where immersion liquid is present. Alternatively, theapparatus has only one table.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g. having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath or only on a localized surface area of the substrate. A liquidsupply system as contemplated herein should be broadly construed. Incertain embodiments, it may be a mechanism or combination of structuresthat provides a liquid to a space between the projection system and thesubstrate and/or substrate table. It may comprise a combination of oneor more structures, one or more liquid inlets, one or more gas inlets,one or more gas outlets, and/or one or more liquid outlets that provideliquid to the space. In an embodiment, a surface of the space may be aportion of the substrate and/or substrate table, or a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.The liquid supply system may optionally further include one or moreelements to control the position, quantity, quality, shape, flow rate orany other features of the liquid.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A lithographic apparatus, comprising: a semi-permeable membrane; aliquid inlet adapted to supply liquid to a first side of the membrane;and a gas inlet adapted to supply to a second side of the membraneeither: (a) a vapor of the liquid; or (b) a gas which dissociates whendissolved in the liquid.
 2. The apparatus of claim 1, wherein thesemi-permeable membrane is in the form of a tube.
 3. The apparatus ofclaim 2, wherein the liquid inlet is adapted to supply liquid inside thetube.
 4. The apparatus of claim 1, wherein the gas inlet is adapted tosupply the vapor or gas at a pressure of less than 1.0 atmosphere. 5.The apparatus of claim 4, wherein the gas inlet is adapted to supply thevapor or gas at a pressure of less than 0.5, 0.1 or 0.05 atmosphere. 6.The apparatus of claim 1, wherein the liquid inlet is adapted to providea flow of liquid past the membrane.
 7. The apparatus of claim 1, whereinthe gas inlet is adapted to provide a flow of gas past the membrane. 8.The apparatus of claim 1, constructed and arranged such that at leastsome liquid which has been provided to the first side is transported toa position between a projection system configured to project a radiationbeam onto a substrate and a substrate such that the radiation beam willpass through the liquid.
 9. The apparatus of claim 1, wherein the liquidis water.
 10. The apparatus of claim 1, wherein the gas is carbondioxide.
 11. The apparatus of claim 1, further comprising a vaporizerconfigured to vaporize the liquid and arranged to provide the vapor ofthe liquid to the gas inlet.
 12. The apparatus of claim 1, wherein theliquid is a top coat.
 13. The apparatus of claim 1, wherein a pressureof the vapor of the liquid on the second side of the membrane is greaterthan the vapor pressure of the liquid, or a pressure of the gas whichdissociates when dissolved in the liquid on the second side of themembrane is greater than the vapor pressure of the liquid.
 14. Theapparatus of claim 1, further comprising an ion exchanger for the liquiddownstream of the membrane.
 15. A device manufacturing method,comprising: transferring a pattern from a patterning device through aliquid onto a substrate, wherein the liquid was provided on one side ofa semi-permeable membrane and a gas provided on another side of thesemi-permeable membrane, the gas being either a vapor of the liquid or agas which dissociates when dissolved in the liquid.
 16. The method ofclaim 15, further comprising transporting at least some of the liquidfrom the one side of the membrane to a position on the substrate priorto exposing the substrate with a beam of radiation.
 17. An apparatusconfigured to de-gas a liquid, the apparatus comprising: asemi-permeable membrane; a pump configured to provide the liquid to afirst side of the membrane; and either (i) a vaporizer configured toprovide vapor of the liquid to a second side of the membrane; or (ii) agas inlet configured to provide a gas which dissociates when dissolvedin the liquid and an ion exchanger for the liquid downstream of thesemi-permeable membrane.
 18. The apparatus of claim 17, wherein thesemi-permeable membrane is in the form of a tube.
 19. The apparatus ofclaim 17, wherein the gas is carbon dioxide.
 20. The apparatus of claim17, wherein a pressure of the vapor of the liquid on the second side ofthe membrane is greater than the vapor pressure of the liquid, or apressure of the gas which dissociates when dissolved in the liquid onthe second side of the membrane is greater than the vapor pressure ofthe liquid.